3D printed zeolite monoliths for CO2 removal

ABSTRACT

Carbon dioxide (CO 2 ) capture materials comprising one or more 3D-printed zeolite monoliths for the capture and or removal of CO 2  from air or gases in enclosed compartments, including gases or mixtures of gases having less than about 5% CO 2 . Methods for preparing 3D-printed zeolite monoliths useful as CO 2  capture materials and filters, as well as methods of removing CO 2  from a gas or mixture of gases in an enclosed compartment using 3D-printed zeolite monoliths are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional application No.62/560,740, entitled “3D Printed Zeolite Monoliths for CO₂ Capture,”filed on Sep. 20, 2017, which is incorporated by reference in itsentirety, for all purposes, herein.

GOVERNMENT SUPPORT CLAUSE

This invention was made with government support under NNX15AK38A awardedby NASA. The government has certain rights in the invention.

FIELD

The present application is directed to compositions for the capture orremoval of carbon dioxide (CO₂) from the air or from CO₂-containinggases or mixtures of gases. Specifically, the present disclosure isdirected to zeolite monoliths configured to capture or remove CO₂, andmethods of preparing and using such compositions.

BACKGROUND

In enclosed environments such as spacecraft or submarine cabins, CO₂levels should be below 0.5% as long-term exposure to CO₂ concentrationsgreater than this level can cause severe health problems such asfatigue, listlessness, malaise, mood changes and headache. Therefore,removal of CO₂ from cabin atmosphere is a critical function of anyspacecraft's or submarine's life support system. In addition, theremoval of CO₂ from indoor air in commercial buildings is gainingsignificant attention among researchers primarily due to the healthrisks associated with elevated CO₂ concentration levels resulting frominadequate ventilation.

The removal of ultra-dilute CO₂, such as ppm CO₂ levels, from enclosedatmospheres is more challenging and energy-intensive than CO₂ capturefrom other industrial gas streams in which CO₂ concentration istypically above 5 vol. %. This is due to the low concentration-gradientdriving force for adsorption at extremely dilute conditions. Moreover,additional considerations related to human health should be taken intoaccount when developing technologies for CO₂ capture from enclosedenvironments. This is particularly important for spacecraft or spacestations where attrition of the adsorbent particles or the release oftoxic chemicals can pose serious health problems to astronauts.

Some current systems for cabin CO₂ removal utilize fixed beds ofadsorbent pellets or beads. These adsorbents may be zeolite 13X or 5Amolecular sieves which are commonly used as benchmark adsorbents for CO₂capture from flue gas streams. As a result of high particle attritionrate, pressure drop builds up in the fixed bed which increases theblower power required to maintain flow, eventually requiring highlyundesirable system maintenance. In such systems, dust fines generatedfrom the attrition propagate downstream and can accelerate failure ratesin downstream components. In order to reduce flow resistance through thefixed bed, pelletization of adsorbent particles with clay binder (orbinderless pellets) may be required. Such pellets are highly porousstructures allowing rapid mass transfer through the pellet. However,this open composite structure tends to have low resistance to attritionand may be weakened by humidity and/or large temperature excursions.Moreover, dusting due to particle attrition in enclosed environments canlead to human health problems such as pneumoconiosis.

Monolithic structures comprising adsorbent particles have beenconsidered as an alternative to conventional packing systems likepellets, beads, or granules. Monolithic structures have been shown toimprove the overall performance in terms of pressure drop and mass andheat transfer characteristics that eventually translate into a low-costand more efficient capture technology while addressing the drawbacks ofconventional packing systems. Monoliths are structured materials withparallel gas flow channels in which the shape and the diameter of theparallel channels and their density per cross sectional area of themonolith are controllable. Traditionally, monoliths are fabricated usingan extrusion process. A particularly challenging aspect to shapeadsorbents into monolithic contactors is the trade-off between keydesign parameters such as active adsorbent loading, mass and heattransfer properties, and cell density (cpsi). While higher adsorbentcontent per unit volume is desirable to achieve higher uptake, thekinetics of adsorption tends to become slower as a result of limitedaccessibility to adsorption sites in thicker walls. In addition, highcell density monoliths that maximize active adsorbent loading andsurface area are preferred but pressure drop through the narrow channelsis substantially higher than through low cell density monoliths.Monolithic adsorbents made of activated carbon, zeolites, andmetal-organic frameworks (MOFs) have been considered as adsorbentstructures for CO₂ capture. For example, cordierite monoliths washcoatedwith a thin layer of 13X zeolite have been investigated experimentallyand numerically for CO₂ capture from flue gas. Although the mechanicalstrength of these coated substrates was found to be reasonably good, theceramic support did not contribute to CO₂ adsorption, hence limiting theactive adsorbent amount per unit volume. Therefore, more robust andhighly efficient adsorbent structures are desired in order to improveCO₂ removal system efficiency and reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present application are described, by way of exampleonly, with reference to the attached Figures, wherein:

FIG. 1 illustrates self-standing cylindrical zeolite 13X monolithshaving square channels and smooth surfaces fabricated by the presentlydisclosed 3D printing method, according to an example embodiment of thepresent disclosure;

FIG. 2A shows N₂ physisorption isotherms for 13X zeolite monolithsprepared using the presently disclosed method, according to an exampleembodiment of the present disclosure;

FIG. 2B illustrates N₂ physisorption isotherms for 5A zeolite monolithsprepared using the presently disclosed method, according to an exampleembodiment of the present disclosure;

FIG. 2C shows pore size distribution curves for 13X zeolite monolithsprepared using the presently disclosed method, according to an exampleembodiment of the present disclosure;

FIG. 2D illustrates pore size distribution curves for 5A zeolitemonoliths prepared using the presently disclosed method, according to anexample embodiment of the present disclosure;

FIG. 3A shows thermogravimetry curves and differential thermogravimetrycurves for calcined and uncalcined R4 13X monoliths, according to anexample embodiment of the present disclosure;

FIG. 3B illustrates thermogravimetry curves and differentialthermogravimetry curves for calcined and uncalcined R4 5A monoliths,according to an example embodiment of the present disclosure;

FIG. 4A illustrates the XRD patterns of calcined monolith 13X-R4 and 13Xpowdered zeolite, according to an example embodiment of the presentdisclosure;

FIG. 4B illustrates the XRD patterns of calcined monolith 5A-R4 and 5Apowdered zeolite, according to an example embodiment of the presentdisclosure;

FIGS. 5A-D show SEM images of the R4 sample of the 13X zeolite monolithwith increasing magnification, according to an example embodiment of thepresent disclosure;

FIGS. 5E-H show SEM images of the R4 sample of the 5A zeolite monolithwith increasing magnification, according to an example embodiment of thepresent disclosure;

FIG. 6 illustrates the compressive strength of monoliths as a functionof zeolite loading (wt %) for (top) 13X zeolite monolith and (bottom) 5A3D-printed monoliths, according to an example embodiment of the presentdisclosure;

FIG. 7 illustrates the CO₂ adsorption capacities for 13X and 5A3D-printed monoliths and zeolite powders obtained at 25° C. using 0.3%and 0.5% CO₂ in N₂, according to an example embodiment of the presentdisclosure;

FIG. 8A illustrates the CO₂ adsorption isotherms for 13X-R4 3D-printedmonoliths and 13X powdered zeolites obtained at 25° C., according to anexample embodiment of the present disclosure;

FIG. 8B illustrates the CO₂ adsorption isotherm for 5A-R4 3D-printedmonoliths and 5A powdered zeolites obtained at 25° C., according to anexample embodiment of the present disclosure;

FIG. 8C illustrates the N₂ adsorption isotherms for 13X-R4 3D-printedmonoliths and 13X powdered zeolites obtained at 25° C., according to anexample embodiment of the present disclosure;

FIG. 8D shows the N₂ adsorption isotherms for 5A-R4 3D-printed monolithsand 5A powdered zeolites obtained at 25° C., according to an exampleembodiment of the present disclosure;

FIG. 9A shows breakthrough curves for 13X-R4 3D-printed zeolitemonoliths as compared to 13X powder zeolite, obtained at 25° C. and 1bar, according to an example embodiment of the present disclosure;

FIG. 9B illustrates breakthrough curves for 5A-R4 3D-printed zeolitemonoliths as compared to 5A powder zeolite, obtained at 25° C. and 1bar, according to an example embodiment of the present disclosure;

FIG. 10A illustrates thermogravimetry and differential thermogravimetrycurves for methyl cellulose, according to an example embodiment of thepresent disclosure;

FIG. 10B illustrates thermogravimetry and differential thermogravimetrycurves for PVA, according to an example embodiment of the presentdisclosure;

FIG. 11 illustrates the X-ray diffraction (XRD) pattern for bentoniteclay, according to an example embodiment of the present disclosure;

FIG. 12A illustrates the stress-strain curves for 13X-R2, 13X-R3, and13X-R4 3D-printed zeolite monoliths, according to an example embodimentof the present disclosure; and

FIG. 12B illustrates the stress-strain curves for 5A-R2, 5A-R3, and5A-R4 3D-printed zeolite monoliths, according to an example embodimentof the present disclosure.

It should be understood that the various aspects are not limited to thearrangements and instrumentality shown in the drawings.

DETAILED DESCRIPTION

It will be appreciated that numerous specific details are set forth inorder to provide a thorough understanding of the embodiments describedherein. However, it will be understood by those of ordinary skill in theart that the embodiments described herein can be practiced without thesespecific details. In other instances, methods, procedures and componentshave not been described in detail so as not to obscure the relatedrelevant feature being described. Also, the description is not to beconsidered as limiting the scope of the embodiments described herein.The drawings are not necessarily to scale and the proportions of certainparts have been exaggerated to better illustrate details and features ofthe present disclosure.

Several definitions that apply throughout this disclosure will now bepresented. The terms “comprising,” “including” and “having” are usedinterchangeably in this disclosure. The terms “comprising,” “including”and “having” mean to include, but are not necessarily limited to, thethings so described.

The present disclosure provides 3D-printed zeolite monoliths and methodsfor their manufacture and use in CO₂ removal from air. 3D-printedzeolite monoliths exhibit excellent mechanical and adsorption propertiesthat render them suitable candidates for not only CO₂ removal fromenclosed environments but also for other adsorption and separationprocesses. Monoliths prepared using 3D printing techniques may havecomplex geometries with unique mechanical and structural properties.Notably, the use of 3D printing techniques allow for preciselyfabricated three-dimensional devices having desired configurations andoptimized properties, as opposed to monoliths prepared usingconventional extrusion processes. High productivity and low fabricationcost are other noticeable advantages of these methods. By employing 3Dprinting techniques, it is possible to fabricate monoliths with variouscross-sections, channel sizes, and wall thicknesses. More importantly,the fabrication parameters can be tuned to obtain parts with highmechanical properties.

According to at least one aspect of the present disclosure, a CO₂capture material is provided. The CO₂ capture material may include oneor more zeolite monoliths. In at least some instances, the zeolitemonolith may consist of a 13X zeolite material or a 5A zeolite materialand one or more binders. The zeolite monolith may be prepared layer bylayer using a 3D printer. The zeolite monolith may comprise at least 80wt % zeolite material, or at least 85 wt % zeolite material, or at least90 wt % zeolite material. In at least some instances, the presentlydisclosed zeolite monoliths may comprise from about 80 wt % to about 90wt % zeolite material. The one or more binders may be selected from thegroup consisting of bentonite clay, methyl cellulose, and anycombination thereof. The one or more binders may comprise from about 7wt % to about 15 wt % of the at least one zeolite monolith. The one ormore binders may be a plasticizing organic binder. The plasticizingorganic binder may comprise from about 2.0 wt % to about 3.5 wt % of thezeolite monolith. In at least some instances, the plasticizing organicbinder may be methyl cellulose. In some instances, the one or morebinders may comprise from about 7 wt % and about 15 wt % bentonite clayand from about 2.0 wt % and about 3.5 wt % methyl cellulose. In at leastsome instances, the zeolite monolith may further include a co-binder. Insome cases, the co-binder may be polyvinyl alcohol. In some instances,the co-binder may comprise from about 1.0 wt % to about 1.5 wt % of thezeolite monolith.

According to at least one aspect of the present disclosure, the zeolitemonolith may exhibit a mesopore volume of at least about 0.009 cm³/g, orof at least about 0.012 cm³/g. In at least some instances, the zeolitemonolith may have a mesoporosity of from about 0.009 cm³/g to about0.020 cm³/g, or from about 0.009 cm³/g to about 0.012 cm³/g, or fromabout 0.012 cm³/g to about 0.020 cm³/g. In at least some instances, thezeolite monolith may have a microporosity of from about 0.22 cm³/g toabout 0.26 cm³/g, or from about 0.18 cm³/g to about 0.26 cm³/g, or fromabout 0.15 cm³/g to about 0.30 cm³/g. In some cases, the zeolitemonolith comprises a wall thickness of from about 0.4 mm to about 0.8mm. In at least some instances, the zeolite monolith comprises a channelwidth of from about 0.2 mm to about 0.6 mm. The presently disclosedzeolite monoliths may exhibit a compression strength of from about 0.30MPa to about 0.69 MPa or from about 0.05 MPa to about 0.35 MPa. Thepresently disclosed zeolite monoliths may also exhibit a Young's modulusof from about 7.50 MPa to about 15.0 Mpa, for 13X zeolite monoliths, orfrom about 1.65 MPa to about 9.45 Mpa for 5A zeolite monoliths.

In at least some instances, the presently disclosed CO₂ capture materialmay include a plurality of zeolite monoliths. The presently disclosedCO₂ capture material and zeolite monoliths are effective at capturingCO₂ from a gas or mixture of gases comprising about 5% or less CO₂.

According to at least one aspect of the present disclosure, a device forremoving CO₂ from a gas or mixture of gases in an enclosed compartmentis provided. The device may include a filter comprising the presentlydisclosed CO₂ capture material and a means for causing a gas or mixtureof gases to contact the filter comprising the CO₂ capture material.

According to at least one aspect of the present disclosure, a method ofpreparing a 3D-printed zeolite monolith is provided. The method mayinclude mixing zeolite powder, bentonite clay, a plasticizing organicbinder, and a co-binder using a high-performance dispersing instrumentat 2500 rpm to obtain a powder mixture. The method may further includeadding a sufficient amount of distilled water to the powder mixture andmixing using the high-performance dispersing instrument at 2500 rpm toform an aqueous paste. The method may further include depositing theaqueous paste layer-by-layer, using a 3D-printing apparatus, onto asubstrate to produce a 3D-printed zeolite monolith. The zeolite powdermay be selected from the group consisting of a 13X zeolite powder and a5A zeolite powder. The inorganic binder may be bentonite clay. In atleast some instances, the plasticizing organic binder may be methylcellulose. In some cases, the co-binder may be polyvinyl alcohol.

According to at least one aspect of the present disclosure, a method forremoving CO₂ from a gas or mixture of gases comprising 5% or less CO₂ isprovided. The method may include bringing a gas or mixture of gasescomprising carbon dioxide in contact with the presently disclosed CO₂capture material and capturing at least a portion of the CO₂ in the gasor mixture of gases in the CO₂ capture material. In some instances theCO₂ is removed from a gas or mixture of gases in an enclosedcompartment. For example, the enclosed compartment may include asubmarine compartment, a spacecraft compartment, a building, or adwelling.

Preparation of Zeolite Monoliths

Self-standing zeolite monoliths may be prepared from zeolite 13X and 5Apowders (UOP), bentonite clay (Sigma Aldrich) as a binder, methylcellulose (Thermo Fisher), as a plasticizing organic binder, andpoly(vinyl) alcohol (PVA, Sigma-Aldrich) as a co-binder. Methylcellulose contains hydroxyl groups that contribute to additionalparticles cohesion while playing an important role in the monolithstrength. A desired amount of these powders may be first mixed using ahigh-performance dispersing instrument IKA-R25 at 2500 rpm. Afterobtaining a homogeneous powder mixture, a sufficient amount of distilledwater may be added and mixed rigorously using the IKA-R25 at 2500 rpmuntil a homogenous aqueous paste with suitable viscosity is produced.The paste is loaded into a syringe (3 mL, Norson EFD, USA) attached to anozzle with a 0.60 mm diameter. In the next step, the paste is extrudedthrough the moving nozzle in a Robocasting 3D printer (3D Inks,Stillwater, Okla., USA). In this method, the printed product is firstdesigned by the software RoboCAD 4.2 that controls the printer motionand then the paste is deposited in a layer by layer fashion with layersbeing perpendicular to each other. Well-defined structures with uniformchannel and layer thickness may be obtained by this method.

FIG. 1 illustrates self-standing cylindrical zeolite 13X monolithshaving square channels and smooth surfaces fabricated by the presentlydisclosed 3D printing method. After the monolithic structures areprinted, they may be initially dried at room temperature to partiallyremove water content. The pieces may then be placed into an oven andheated at 100° C. to remove the rest of water and allow the polymerlinker (PVA) and methyl cellulose to quickly build up high strength andavoid skin cracking. After drying in the oven, the monoliths may becalcined (sintered) at 700° C. at the rate of 20° C./min in atemperature-controlled furnace for 2-4 hours in order to decompose andremove the co-binders, methyl cellulose and PVA. This calcination stepremoves the organic content and results in increasing the mesoporosityin addition to enhancing the mechanical strength of the final calcinedmonolith.

In order to determine the mechanical stability and CO₂ adsorptionperformance of monolithic structures, zeolite 13X and 5A monoliths wereprepared by varying the zeolite to binder weight ratio, co-binder andplasticizer concentrations. Table 1 shows the compositions of the3D-printed 13X and 5A monoliths prepared according to the presentlydisclosed method.

TABLE 1 Compositions of the fabricated 3D-printed 13X and 5A zeolitemonoliths. Zeolite Bentonite clay Methyl cellulose Monolith (wt %) (wt%) (wt %) PVA (wt %) R2 80 15 3.5 1.5 R3 85 10 3.5 1.5 R4 90 7 2.0 1.0Characterization of Zeolite Monoliths

The textural properties of the zeolites in both powder and monolithforms were determined by collecting N₂ physisorption isotherms at 77 Kusing a Micromeritics 3Flex gas analyzer. All samples were firstdegassed on a Micromeritics PreVac at 350° C. for 8 hours beforemeasurement. The obtained isotherms were used to evaluate the surfacearea pore volumes, and pore size distribution (PSD). The X-raydiffraction (XRD) measurements were conducted using PANalytical X′PertMultipurpose X-ray Diffractometer with scan step size of 0.02°/step atthe rate of 147.4 s/step. Structural morphology was studied by Hitachi54700 Field Emission Scanning Electron Microscopy (SEM). In order toobtain cross sectional view in SEM, monolith structures were placedhorizontally on the sampler holder and their height was adjustedaccordingly. To measure the residual binder content that remains in themonolith after calcination, TGA-DSC was carried out from 25 to 700° C.at the rate of 20° C./minute using TGA (Q500, TA Instruments).

Mechanical Testing

Mechanical testing was carried out using an Instron 3369 (Instron,Norwood, USA) mechanical testing device. Initially, monoliths werepolished with a 3M surface smoothing sand paper to prevent uncertainsurface and to avoid cracks on the surface for achieving effectiveresults. After polishing, the monolith was placed between two metalplates and compressed with 500 N load cell at 2.5 mm/minute while theapplied load and piston movement was recorded, following the ASTMD4179-01 (standard test method for single pellet crush strength offormed catalyst shapes) procedure. The compressive force was applieduntil the monolith broke.

Adsorption Capacity Measurements

TGA (Q500, TA Instruments) was utilized to measure CO₂ capacity underultra-dilute capture conditions. To drive off the pre-adsorbed gases,moisture or any other impurities, commercial powders and synthesizedmonoliths were first degassed at 400° C. under N₂ with the flow rate of40 mL/minute. CO₂ capture uptake measurements were then carried out atroom temperature by exposing the samples to 0.5% CO₂ in N₂. In addition,the CO₂ and N₂ adsorption isotherms for R4 monoliths and their powdercounterparts were measured by 3Flex at 25° C.

CO₂ Breakthrough Experiments

Breakthrough experiments were performed in a small-scale fixed-bedcolumn coupled with a BEL-Mass spectrometer (MS). The feed stream with acomposition of 0.5% CO₂/N₂ was fed into the column at a flow rate of 60mL/min. Prior to each sorption experiment, the bed was heated to 400° C.under flowing N₂ at 60 mL/min for 2 hours to desorb adventitious CO₂ andwater, then cooled to 25° C. and exposed to CO₂ for the experimentalsorption run. The effluent composition exiting the column wastransiently measured by the MS and after reaching the inletconcentration, the desorption step was started by flowing N₂ to thecolumn at the same flowrate (i.e., 60 mL/min).

Physical Properties of 3D-Printed Monoliths

FIG. 2A-D illustrates N₂ physisorption isotherms and the correspondingpore size distribution curves, for the presently disclosed 13X and 5Azeolite monoliths. FIG. 2A shows N₂ physisorption isotherms for 13Xzeolite monoliths prepared according to the presently disclosed methods.FIG. 2B illustrates N₂ physisorption isotherms for 5A zeolite monolithsprepared according to the presently disclosed methods. FIG. 2C showspore size distribution curves for 13X zeolite monoliths preparedaccording to the presently disclosed methods, while FIG. 2D illustratespore size distribution curves for 5A zeolite monoliths preparedaccording to the presently disclosed methods. The pore size distributionwas derived from the DFT method using the desorption branch of the N₂isotherm.

The N₂ physisorption isotherms and the corresponding pore sizedistribution curves, shown in FIG. 2A-D, were used to assess theporosity of the monoliths and their powder analogues. For the monolithicsamples, the isotherms show an initial steep uptake at low partialpressures (P/P₀) between 0.0 and 0.05 corresponding to the adsorption inthe micropores, followed by a gradual increase with hysteresis at highP/P₀ indicative of capillary condensation in mesopores. The N₂ isothermsfor 3D-printed 13X and 5A monoliths are of type IV isotherm shape whilethe powder zeolites displayed a typical type I isotherm shapecharacteristic of microporous materials.

Table 2 summarizes the BET surface area, micropore and mesopore volumes,and the corresponding diameters of 3D-printed monoliths preparedaccording to the present disclosure, as well as zeolite powders. The BETsurface areas of 13X-R4 and 5A-R4 monoliths were found to be 635 and 543m²/g, respectively whereas the micropore volumes (at P/P₀=0.99) werecalculated to be 0.24 and 0.25 cm³/g, respectively. As shown in Table 2,all of these BET values were relatively lower than those for zeolite 13Xand 5A in the powder form, as expected due to the lower zeolite content.The data presented in Table 2 also shows that the characteristics of the13X and 5A monoliths were very similar. Although increasing the bindercontent resulted in reduced BET surface area and micropore volume, themesopore volume increased with binder content. Notably, the mesoporevolume of 13X monolith was higher than that of the 5A monoliths withsimilar composition (0.020 compared to 0.014 cm³/g). It should be notedhere that for the rest of our analysis we only focused on the monolithswith highest zeolite loading (R4) and compared their characteristicswith their powder counterparts.

TABLE 2 N₂ physisorption data for 3D-printed monoliths and zeolitepowders. S_(BET) ^([a]) V_(micro) ^([b]) V_(meso) ^([c]) d_(micro)^([d]) d_(meso) ^([d]) Sample (m²/g) (cm³/g) (cm³/g) (nm) (nm) Powderzeolite 13X 770 0.31 — 1.06 — Monolith 13X-R2 498 0.22 0.020 1.06 2.5,4, 6.3, 7.8 Monolith 13X-R3 517 0.25 0.018 1.06 2.8, 3, 3.6, 4.2, 6.8Monolith 13X-R4 571 0.26 0.012 1.06 4.3 Powder zeolite 5A 705 0.29 —1.07 — Monolith 5A-R2 395 0.18 0.014 1.07 2.6, 3.2, 3.8, 4, 6.7 Monolith5A-R3 504 0.23 0.012 1.07 2.8, 3.6 Monolith 5A-R4 543 0.25 0.009 1.072.5, 3.2 ^([a])Obtained at P/P₀ in the range of 0.05-0.3.^([b])Estimated by t-plot. ^([c])Estimated by subtracting V_(micro) fromthe total volume at P/P₀ = 0.99. ^([d])Estimated using Horvath-Kawazoemethod.

As shown in Table 2, the size of the micropores calculated using the DFTmethod was 1.06 nm for 13X-R4 and 1.07 nm for 5A-R4 monoliths. For allmaterials, the first peak appears in the range from 0.5 to 2 nm whichcorresponds to micropore range. For 13X-R2 and 13X-R3 zeolite monoliths,the meso-sized pores were obtained in the range of from about 20 nm to25 nm. This difference in the mesopore size distribution may beattributed to short heating and stirring time. As expected, shapingzeolite particles into a self-standing monolith configuration using 3Dprinting method introduces mesoporosity into the structure. In addition,the formed mesopores in the monolith R2 monoliths are bigger in sizethan in the R3 and R4 monoliths mainly due to the smaller amounts ofbinder and plasticizer in the later samples.

After forming a paste, the function of the plasticizer is no longernecessary and to achieve better mass transfer and the formation ofsecondary pore structure, removal of plasticizer is processed bycalcination. Upon calcination, the organic content of the monolith(i.e., methyl cellulose and PVA) was removed rendering the calcinedmonoliths containing zeolite and binder particles only. To verify this,the amounts of zeolite and bentonite clay were quantified by TGA.

FIGS. 3A-B illustrates thermogravimetry curves and differentialthermogravimetry curves for as-synthesized (uncalcined) and calcinedzeolite monoliths for the highly loaded R4 sample. Specifically, FIG. 3Ashows the thermogravimetry curves and differential thermogravimetrycurves for calcined and uncalcined R4 13X monoliths while FIG. 3Billustrates thermogravimetry curves and differential thermogravimetrycurves for calcined and uncalcined R4 5A monoliths. As shown in FIG. 10,TGA data of methyl cellulose and PVA indicated a weight loss step at360° C. and 275° C., respectively. On the basis of these profiles, it isbelieved that the weight losses below 200° C. correspond to moisturedesorption. For uncalcined monoliths, the other weight losses appearingbetween 200° C. and 700° C. are associated with the decomposition oforganic additives, whereas for calcined samples, small weigh lossescould be attributed to the loss of organic compounds that had beentrapped in the pore network during the sintering process and stillexisted in the structure after calcination. The total weight lossbetween 200° C. and 700° C. was 10 wt % and 8 wt % for uncalcined 13X-R4and 5A-R4 calcined monoliths, respectively, while both samples exhibited˜4 wt % weight loss after calcination. The later implies that the totalweight of zeolite and permanent binder (bentonite clay) in the finalmonoliths is ˜96 wt % which is close to the nominal weight fractionsused in the preparation step (see Table 1).

Structural Properties of 3D-Printed Monoliths

FIGS. 4A-B illustrates the XRD patterns of 13X-R4 and 5A-R4 zeolitemonoliths after calcination along with their powder counterparts.Specifically, FIG. 4A shows the XRD patterns of calcined monolith 13X-R4and 13X powdered zeolite, while FIG. 4B illustrates the XRD patterns ofcalcined monolith 5A-R4 and 5A powdered zeolite. As depicted in FIGS.4A-B, good crystallinity of the zeolites was retained although slightdifferences in the peak intensities can be observed in the XRD patternsof 3D-printed monoliths with 90 wt % zeolite loading. This could beattributed to the presence of the binder (bentonite clay) or the changein the size of zeolite particles as a result of sintering during thecalcination process. In addition, these patterns reveal that thediffraction peaks of FAU and LTA frameworks were retained in themonolithic structures. The presence of peaks at 2=6.2°, 15.6°, and 30.9°in FIG. 4A correspond to (111), (331), and (715) planes in FAUframework, respectively whereas the reflections at 2=7.2°, 16.1°, and27.1° in FIG. 4B are related to (200), (420), and (642) planes in LTAframework. It is worth mentioning that the low intensity diffractionspeaks of bentonite clay, as shown in FIG. 11, appeared at 2˜20 and 27°and were overlapped with those of zeolites at the same angle.

Low and high magnification scanning electron microscope (SEM) images of13X-R4 and 5A-R4 monoliths prepared according to the presently disclosed3D printing technique are presented in FIGS. 5A-H. Specifically, FIGS.5A-D show SEM images of the R4 sample of the 13X zeolite monolith withincreasing magnification, while FIGS. 5E-H show SEM images of the R4sample of the 5A zeolite monolith with increasing magnification. The lowmagnification SEM images shown in FIG. 5A and FIG. 5E reveal the uniformsquare channel cross-section of the structures with a wall thickness of˜0.65 mm and channel width of ˜0.4 mm for both the 13X and 5A zeolitemonoliths. The magnified views of the channel structures shown in FIGS.5B-D and FIGS. 5F-H clearly illustrate the macroporous nature of thewalls with pores on the order of 5-50 μm. These images indicate that the3D-printed monoliths retained their porous morphology and that theparticles sintered together to form a porous network with voids havingsizes on the scale of micrometers. Moreover, it is apparent from theseimages that the particle distribution was not adversely affected by thepaste preparation and printing conditions, and no particlesagglomeration could be observed.

Mechanical Strength of 3D-Printed Monoliths

The mechanical strength and deformation of the samples were assessed bya compression test. FIG. 6 illustrates the compressive strength ofmonoliths as a function of zeolite loading (wt %) for (FIG. 6 top) 13Xzeolite monolith and (FIG. 6 bottom) 5A 3D-printed monoliths. Inaddition, the corresponding compressive strength and the average Young'smodulus values extracted from this data are presented in Table 3. Thetrend in FIG. 6 (top) suggests a proportional relationship betweenzeolite loading and compressive strength and also the displacementbetween particles that the material tends to retain upon loading,relative to the length of the monolith. The 13X-R4 sample, containingthe highest zeolite loading (90 wt %), showed maximum compressivestrength (0.69 MPa) before catastrophic failure which can be attributedto its porosity and microporous texture. Since a smaller amount ofbinder and additives were used in the preparation of 13X-R4, thismonolith is denser than the 13X-R3 and 13X-R2 samples and itsmicroporous texture requires high compressive force to deform microporewalls as compared to 13X-R3 and 13X-R2. In contrast, 13X-R2 exhibitedthe lowest compressive strength (0.3 MPa) as a result of higher mesoporevolume than other monoliths.

TABLE 3 Mechanical testing data for 3D-printed monoliths. Compressionstrength Young's modulus Sample (MPa) (MPa) Monolith 13X-R2 0.30 7.50Monolith 13X-R3 0.45 10.0 Monolith 13X-R4 0.69 15.0 Monolith 5A-R2 0.051.65 Monolith 5A-R3 0.17 5.75 Monolith 5A-R4 0.35 9.45

FIG. 6 (bottom) illustrates the compressive strength of 5A-R2, 5A-R3 and5A-R4 monoliths. As depicted in FIG. 6 (bottom), the compressivestrength data shows a similar increasing trend with zeolite loading asfor the 13X monoliths. However, compressive strengths of the 5Amonoliths were much lower than that of 13X monoliths with the samezeolite loading which could be linked to their less dense structure.Maximum compressive stresses of 0.35, 0.15 and 0.5 MPa were recorded for5A-R4, 5A-R3 and 5A-R2, respectively (see Table 3). The correspondingstress-strain curves are also shown in FIGS. 12A-B. Comparing the crushstrength of the monoliths with that of 5A pellets used in NASA's CO₂removal system revealed that the 3D monoliths have higher crush strengththan the pellets. However, it should be noted that the single pelletcrush tests on the NASA's 5A pellets were performed under humidconditions which could be a reason for having lower strength.

Equilibrium Adsorption Measurements

The CO₂ adsorption capacity of 3D-printed monoliths was determined byTGA experiments at 25° C. and two different concentrations, namely 0.3%and 0.5% relevant to the CO₂ partial pressure in enclosed environments.FIG. 7 illustrates the CO₂ adsorption capacities for 13X and 5A3D-printed monoliths and zeolite powders obtained at 25° C. using 0.3%and 0.5% CO₂ in N₂. As depicted in FIG. 7, the zeolite monolithsprepared by the presently disclosed 3D printing technique exhibitcomparable capacity to the powder zeolites. In particular, for 0.5%CO₂/N₂, 13X-R4 showed a CO₂ uptake of 1.39 mmol/g which is 87% of thatof 13X zeolite in the powder form, whereas, 5A-R4 exhibited 89% of thecapacity of the 5A powder (1.43 mmol/g). Moreover, as can be seen fromthese results, increasing the zeolite/binder weight ratio resulted inthe increased CO₂ adsorption capacity. This expected proportional CO₂adsorption to zeolite loading in monolithic adsorbents could beattributed to the fact that equilibrium adsorption mainly takes place inmicropores of the monoliths. Analyzing the micropore volumes ofmonoliths obtained from N₂ physisorption (Table 2) and CO₂ adsorptioncapacities (FIG. 7), it follows that the difference in adsorption uptakeof monoliths are proportional to the difference in their microporevolumes. For instance, the adsorption capacity of 5A-R4 was 1.12 timeshigher than that of 5A-R3, while its micropore volume was 1.10 timeshigher.

In addition to single point adsorption measurements, pure CO₂ and N₂adsorption isotherms were obtained at 25° C. and 1 bar, as shown inFIGS. 8A-D. Specifically, FIG. 8A illustrates the CO₂ adsorptionisotherms for 13X-R4 3D-printed monoliths and 13X powdered zeolitesobtained at 25° C. FIG. 8B illustrates the CO₂ adsorption isotherm for5A-R4 3D-printed monoliths obtained at 25° C. FIG. 8C illustrates the N₂adsorption isotherms for 13X-R4 3D-printed monoliths and 13X powderedzeolites obtained at 25° C. FIG. 8D shows the N₂ adsorption isothermsfor 5A-R4 3D-printed monoliths and 5A powdered zeolites obtained at 25°C.

The monoliths exhibited similar behavior to their powder counterparts,displaying high affinity towards CO₂ with negligible N₂ adsorption.Consistent with TGA tests, the CO₂ isotherms for 3D-printed monolithswere comparable to those for zeolite powders. The monoliths 13X-R4 and5A-R4 displayed a sharp CO₂ uptake at low pressures reaching 88% and 75%of their equilibrium capacities at 0.2 bar, respectively, followed bygradual increase until full equilibrium at higher pressures was reached.Compared to other self-standing zeolite monoliths in the art, thepresently disclosed 3D-printed monoliths show higher CO₂ uptake at roomtemperature.

CO₂ Breakthrough Experiments

The dynamic adsorption performance of the presently disclosed zeolitemonoliths and powders were evaluated at 25° C. and atmospheric pressureusing a feed gas containing 0.5% CO₂ in N₂ with the flow rate of 60mL/min. FIGS. 9A-B illustrate the corresponding CO₂ breakthroughprofiles. Specifically, FIG. 9A shows breakthrough curves for 13X-R43D-printed zeolite monoliths as compared to 13X powder zeolite, obtainedat 25° C. and 1 bar. FIG. 9B illustrates breakthrough curves for 5A-R43D-printed zeolite monoliths as compared to 5A powder zeolite, obtainedat 25° C. and 1 bar.

For both 13X and 5A, the zeolite powders retained CO₂ longer andexhibited longer breakthrough times than their monolithic counterparts.However, the concentration fronts of 13X-R4 and 5A-R4 monoliths weresharper than those of powders with the breakthrough width of 36 minutesand 61 minutes, respectively (compared to 40 minutes and 75 minutes, for13X and 5A powders, respectively) indicating less mass transferresistance in monolithic beds. Here breakthrough width is defined as thedifference between the time to reach 5% and 95% of the finalcomposition. Table 4 tabulates the breakthrough times for the samplesalong with times to reach 50% and 95% of final concentration.Importantly, the dynamic capacities could be correlated to the zeoliteloading and hence equilibrium adsorption capacity of the monoliths. The13X powder attained 50% of the final concentration at 23 min which was1.2 times longer than the time for 13X-R4 (23 minutes). This can beattributed to the difference in zeolite loading of the samples with 13Xpowder having 1.1 higher loading than the 13X monolith (see Table 1).The same trend could be realized for 5A samples.

TABLE 4 data for 3D-printed monoliths and zeolite powders. Breakthrought_(5%) t_(50%) t_(95%) width Sample (min) (min) (min) (min) Powderzeolite 13X 13 23 53 40 Monolith 13X-R4 9 19 48 36 Powder zeolite 5A 1544 90 75 Monolith 5A-R4 9 36 70 61

The presently disclosed 13X and 5A zeolite monoliths with high zeolitecontent, fabricated according to the presently disclosed 3D printingtechniques, comprise a network of interconnected micro, meso, andmacropores of zeolite and binder particles, and are thus characterizedby macro-meso-microporosity. Such macro-meso-microporous zeolitemonoliths comprise a plurality of micropores having a diameter ofgreater than 15 nanometers and a plurality of mesopores having adiameter of from 2 nanometers to 15 nanometers. The presently disclosed3D-printed zeolite monoliths, having macro-meso-microporosity, havesurprisingly been found to exhibit unexpectedly high CO₂ adsorption andmechanical strength characteristic of improved CO₂ removal materials.The 3D-printed 5A and 13X monoliths with high zeolite loading (90 wt %)showed comparable CO₂ adsorption to their powder counterparts. Moreimportantly, these novel structures gave rise to improved adsorptioncapacity and mechanical stability. By using 3D printing technique, it ispossible to systematically tune the porosity, zeolite loading, andmechanical strength of monolithic structures. The presently disclosedCO₂ capture materials and 3D printing methods offers an alternativeapproach for fabricating CO₂ adsorbent materials in any configurationsthat can be used for various adsorptive-based separation processes.

Statements of the Disclosure Include:

Statement 1: A CO₂ capture material comprising one or more zeolitemonoliths, the one or more zeolite monoliths comprising: a zeolitematerial selected from the group consisting of a 13X zeolite materialand a 5A zeolite material; and one or more binders.

Statement 2: A CO₂ capture material according to Statement 1, whereinthe zeolite monolith is prepared layer by layer using a 3D printer.

Statement 3: A CO₂ capture material according to Statement 1 orStatement 2, wherein the at least one zeolite monolith comprises atleast 80 wt % zeolite material.

Statement 4: A CO₂ capture material according to Statement 1 orStatement 2, wherein the at least one zeolite monolith comprises atleast 85 wt % zeolite material.

Statement 5: A CO₂ capture material according to Statement 1 orStatement 2, wherein the at least one zeolite monolith comprises atleast 90 wt % zeolite material.

Statement 6: A CO₂ capture material according to any one of thepreceding Statements 1-5, wherein the one or more binders is selectedfrom the group consisting of bentonite clay, methyl cellulose, and anycombination thereof.

Statement 7: A CO₂ capture material according to any one of thepreceding Statements 1-6, wherein the one or more binders comprises fromabout 7 wt % to about 15 wt % of the one or more zeolite monoliths.

Statement 8: A CO₂ capture material according to any one of thepreceding Statements 1-7, wherein the one or more binders comprises aplasticizing organic binder.

Statement 9: A CO₂ capture material according to Statement 8, whereinthe plasticizing organic binder comprises from about 2.0 wt % to about3.5 wt % of the one or more zeolite monoliths.

Statement 10: A CO₂ capture material according to Statement 8 orStatement 9, wherein the plasticizing organic binder is methylcellulose.

Statement 11: A CO₂ capture material according to any one of thepreceding Statements 1-10, wherein the one or more zeolite monolithsfurther comprises a co-binder.

Statement 12: A CO₂ capture material according to Statement 11, whereinthe co-binder is polyvinyl alcohol.

Statement 13: A CO₂ capture material according to Statement 11 orStatement 12, wherein the co-binder comprises from about 1.0 wt % toabout 1.5 wt % of the one or more zeolite monoliths.

Statement 14: A CO₂ capture material according to any one of thepreceding Statements 1-13, wherein the one or more binders comprisesfrom about 7 wt % and about 15 wt % bentonite clay and from about 2.0 wt% and about 3.5 wt % methyl cellulose.

Statement 15: A CO₂ capture material according to any one of thepreceding Statements 1-14, wherein the one or more zeolite monolithscomprises a mesopore volume of at least about 0.009 cm³/g.

Statement 16: A CO₂ capture material according to any one of thepreceding Statements 1-14, wherein the one or more zeolite monolithsexhibits a mesopore volume of at least about 0.012 cm³/g.

Statement 17: A CO₂ capture material according to any one of thepreceding Statements 1-14, wherein the one or more zeolite monolithscomprises a mesoporosity of from about 0.009 cm³/g to about 0.020 cm³/g.

Statement 18: A CO₂ capture material according to any one of thepreceding Statements 1-14, wherein the one or more zeolite monoliths hasa mesoporosity of from about 0.009 cm³/g to about 0.012 cm³/g.

Statement 19: A CO₂ capture material according to any one of thepreceding Statements 1-14, wherein the one or more zeolite monoliths hasa mesoporosity of from about 0.012 cm³/g to about 0.020 cm³/g.

Statement 20: A CO₂ capture material according to any one of thepreceding Statements 1-19, wherein the one or more zeolite monolithscomprises a wall thickness of from about 0.4 mm to about 0.8 mm.

Statement 21: A CO₂ capture material according to any one of thepreceding Statements 1-20, wherein the one or more zeolite monolithscomprises a channel width of from about 0.2 mm to about 0.6 mm.

Statement 22: A CO₂ capture material according to any one of thepreceding Statements 1-21, wherein the one or more zeolite monolithsexhibits a compression strength of from about 0.30 MPa to about 0.69MPa.

Statement 23: A CO₂ capture material according to any one of thepreceding Statements 1-21, wherein the one or more zeolite monolithsexhibits a compression strength of from about 0.35 MPa to about 0.69MPa.

Statement 24: A CO₂ capture material according to any one of thepreceding Statements 1-23, wherein the one or more zeolite monolithsexhibits a Young's modulus of from about 7.50 MPa to about 15.0 MPa orfrom about 1.65 MPa to about 9.45 MPa.

Statement 25: A CO₂ capture material according to any one of thepreceding Statements 1-24, wherein the one or more zeolite monoliths ischaracterized by the X-ray diffraction (XRD) pattern shown in FIG. 4A orFIG. 4B.

Statement 26: A CO₂ capture material according to any one of thepreceding Statements 1-25, wherein the one or more zeolite monoliths ischaracterized by the thermogravimetry curves or differentialthermogravimetry curves shown in FIG. 3A or FIG. 3B.

Statement 27: A CO₂ capture material according to any one of thepreceding Statements 1-26, wherein the one or more zeolite monoliths ischaracterized by the pore size distribution curves shown in FIG. 2C orFIG. 2D.

Statement 28: A CO₂ capture material according to any one of thepreceding statements 1-27, comprising a plurality of zeolite monoliths.

Statement 29: A CO₂ capture material according to any one of thepreceding Statements 1-28, wherein the one or more zeolite monoliths iseffective at capturing CO₂ from a gas or mixture of gases comprisingabout 5% or less CO₂.

Statement 30: A CO₂ capture material comprising one or more zeolitemonoliths characterized by the X-ray diffraction (XRD) pattern shown inFIG. 4A or FIG. 4B.

Statement 31: A CO₂ capture material comprising one or more zeolitemonoliths characterized by the thermogravimetry curves or differentialthermogravimetry curves shown in FIG. 3A or FIG. 3B.

Statement 32: A CO₂ capture material comprising one or more zeolitemonoliths characterized by the pore size distribution curves shown inFIG. 2C or FIG. 2D.

Statement 33: A device for removing CO₂ from a gas or mixture of gasesin an enclosed compartment, the device comprising: a filter comprising aCO₂ capture material according to any one of claims 1-32; and a meansfor causing a gas or mixture of gases to contact the filter comprising aCO₂ capture material.

Statement 34: A method of preparing a 3D-printed zeolite monolith, themethod comprising: mixing zeolite powder, bentonite clay, a plasticizingorganic binder, and a co-binder using a high-performance dispersinginstrument at 2500 rpm to obtain a powder mixture; adding a sufficientamount of distilled water to the powder mixture and mixing using thehigh-performance dispersing instrument at 2500 rpm to form an aqueouspaste; and depositing the aqueous paste layer-by-layer, using a3D-printing apparatus, onto a substrate to produce a 3D-printed zeolitemonolith.

Statement 35: A method according to Statement 34, wherein the zeolitepowder is selected from the group consisting of a 13X zeolite powder anda 5A zeolite powder.

Statement 36: A method according to Statement 34 or Statement 35,wherein the plasticizing organic binder is methyl cellulose.

Statement 37: A method according to any one of the preceding Statements34-36, wherein the co-binder is polyvinyl alcohol.

Statement 38: A method for removing CO₂ from a gas or mixture of gasescomprising 5% or less CO₂, the method comprising: bringing a gas ormixture of gases comprising carbon dioxide in contact with a CO₂ capturematerial according to any one of claims 1-32; and capturing at least aportion of the CO₂ in the gas or mixture of gases in the CO₂ capturematerial.

Statement 39: A method according to Statement 38, wherein CO₂ is removedfrom a gas or mixture of gases in an enclosed compartment.

Statement 40: A method according to Statement 39, wherein the enclosedcompartment is selected from the group consisting of a submarinecompartment, a spacecraft compartment, a building, and a dwelling.

We claim:
 1. A method of preparing a 3D-printed zeolite monolith, themethod comprising: mixing zeolite powder, bentonite clay, a plasticizingorganic binder, and an organic co-binder using a high-performancedispersing instrument at 2500 rpm to obtain a powder mixture; adding asufficient amount of distilled water to the powder mixture and mixingusing the high-performance dispersing instrument at 2500 rpm to form anaqueous paste; and depositing the aqueous paste layer-by-layer, using a3D-printing apparatus, onto a substrate to produce a 3D-printed zeolitemonolith.
 2. The method according to claim 1, wherein the zeolite powderis selected from the group consisting of a 13X zeolite powder and a 5Azeolite powder.
 3. The method according to claim 1, wherein theplasticizing organic binder is methyl cellulose.
 4. The method accordingto claim 1, wherein the organic co-binder is polyvinyl alcohol.
 5. Themethod according to claim 1, wherein a combined amount of plasticizingorganic binder and organic co-binder comprises from about 3 weightpercent to about 5 weight percent of the 3D-printed zeolite monolith. 6.The method according to claim 1, wherein the 3D-printed zeolite monolithcomprises from about 80 weight percent to about 90 weight percentzeolite powder.
 7. The method according to claim 5, wherein the3D-printed zeolite monolith comprises from about 7 weight percent toabout 15 weight percent bentonite clay.
 8. The method according to claim7, wherein the 3D-printed zeolite monolith comprises from about 2.0weight percent to about 3.5 weight percent plasticizing organic binder.9. The method according to claim 8, wherein the 3D-printed zeolitemonolith comprises from about 1.0 weight percent to about 1.5 weightpercent organic co-binder.
 10. The method according to claim 1, furthercomprising: calcining the 3D-printed zeolite monolith so as tosubstantially remove the plasticizing organic binder and the organicco-binder to generate a zeolite monolith comprising microporosity,mesoporosity, and microporosity.